A Power over Ethernet (PoE) system includes power sourcing equipment (PSE) and a powered device (PD). The PSE supplies power to the PD while communicating with the PD through an Ethernet twisted pair. The Ethernet twisted pair includes eight cables numbered 1 to 8. A cable 1 and a cable 2 are paired, a cable 3 and a cable 6 are paired, a cable 4 and a cable 5 are paired, and a cable 7 and a cable 8 are paired. Two paired cables are twisted together. In a widely used 100 M Ethernet, a cable pair 1-2 and a cable pair 3-6 are used for communication, and a cable pair 4-5 and a cable pair 7-8 are idle. Therefore, the cable pair 1-2 and the cable pair 3-6 form a group, and the cable pair 4-5 and the cable pair 7-8 form another group. A data cable pair group (a cable pair 1-2 and a cable pair 3-6) is usually used for early Power over Ethernet supply. Two groups of cable pairs can be used together for new Power over Ethernet supply. FIG. 1 shows a structure of a PD. The PD in FIG. 1 uses a diode full-bridge rectifier circuit.
A power loss of diodes is large. Therefore, power utilization of the PD is low.